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Farmall & IHC Tractors Discussion Forum

compression

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norman koch

06-27-2007 11:09:49

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what should the compression be for a 1953 Super M? My manual says a ratio of 5.9/1, which is only 88PSI. thanks in advance norm

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Rootsy

06-28-2007 06:06:48

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Re: compression in reply to norman koch, 06-27-2007 11:09:49

My M w/ 4" Firecraters and an 8060 head pushes 140 psi.

Straight pressure ratios are one thing but the issue within an engine is; the timing of the intake and exhaust events. you do not get complete volume filling on the intake stroke and therefore will not get a true pressure reading as assuming all the cylinder space is filled at BDC. It is all about volumetric efficiency.

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BDM

06-27-2007 19:12:14

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Re: compression in reply to norman koch, 06-27-2007 11:09:49

Buddies SM has 180 psi, but he did a few things :-)

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El Toro

06-27-2007 18:58:12

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Re: compression in reply to norman koch, 06-27-2007 11:09:49

I think you should have around 125psi on all cylinders or within a few pounds of the readings. Good compression is determined by good piston rings sealing, sleeves not worn and valves that are seating good and not leaking. Hal

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CGtractor

06-27-2007 18:33:40

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Re: compression in reply to norman koch, 06-27-2007 11:09:49

I recently bought a 1952 M at an auction. It had been sitting for years but wasn't locked up. After getting it running I checked compression, it had 125 on all 4 cylinders. I have no idea what pistons or head it has.

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champspa

06-27-2007 16:11:19

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Re: compression in reply to norman koch, 06-27-2007 11:09:49

go to Weber's tractor they have the original specs

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Janicholson

06-27-2007 16:01:20

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Re: compression in reply to norman koch, 06-27-2007 11:09:49

The compression ratio is a volume factored math problem, Swept volume (Area of piston X Stroke) expressed as a ratio to cylinder head volume. It can, but often does not, predict compression pressure. If the intake was wide open, and the spark plugs out, and the starter good, I would expect in the area od 100PSI on an unmodified SM. The "farm fuels" were low in octane, and IH could not afford hundereds or thousands of burnt pistons. JimN

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A. Bohemian

06-27-2007 16:32:40

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Thanks, Jim. in reply to Janicholson, 06-27-2007 16:01:20

Quote: "Swept volume (Area of piston X Stroke) expressed as a ratio to cylinder head volume. It can, but often does not, predict compression pressure."

An excellent, concise explanation; I get it now.

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Lawmar

06-27-2007 14:48:30

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Re: compression in reply to norman koch, 06-27-2007 11:09:49

I just bought a Super M with the 8574 (same as 8060) head and it has 4.125 IH fire crater pistons and 120 PSI straight on all 4 cylinders.

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Charles McNelly

06-27-2007 19:40:30

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Re: compression in reply to Lawmar, 06-27-2007 14:48:30

My W-6 with 3 7/8" flat tops and a 8060 head has 110 to 120 lbs. I would really like to see somewhere 200+. I think it would help with that sled I try to pull. Charles

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A. Bohemian

06-27-2007 12:39:09

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You'd THINK So... in reply to norman koch, 06-27-2007 11:09:49

...if you extrapolate out the usual air pressure of 15 lbs. or so per square inch given at sea level.

But it doesn't work out that way, for some reason. You ideally want over a hundred pounds per square inch (and no more than a few pounds difference between cylinders). Many of those who post on these boards (myself included) would be thinking SERIOUSLY about a rebuild at much below 90 lbs. per square inch, no matter how well the tractor seemed to be running.

It's one of those things I've never learned the reason for. Maybe someone professionally trained (or just smarter than I) can explain why.

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dej(jed)

06-27-2007 11:30:42

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Re: compression in reply to norman koch, 06-27-2007 11:09:49

Mine has 125 psi more or less. I have a couple of others that are lower at around 100 psi. It has a lot to do with rings and bore etc.

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